The purpose of a centre-tap transformer in a full-wave rectifier is to:
**Rectifier** converts AC to DC using diode unilateral conduction, half-wave conducts only during positive half-cycle when forward biased, output pulsating DC with frequency equal to input 50 Hz, full-wave with centre-tap uses two diodes conducting alternate half-cycles, output frequency 100 Hz for 50 Hz input, 120 Hz for 60 Hz input, output voltage closer to peak with capacitor filter. The centre-tap transformer splits the secondary voltage into two equal halves, allowing two diodes to rectify alternate half-cycles, producing a full-wave output. Substituting values gives Split the AC input, w
Ref: NCERT > Physics Book > Electronic Devices > Rectifiers, Filters and Applications